Just for fun, I was curious to see what it would be like,
performance-wise, to simulate a synchronized mutable hash map by
putting a clojure hash map inside an atom, and making this accessible
to Java code via the map interface.
I didn't try to implement the entire map interface, but just the major
things for testing purposes. The code is below.
Benchmarking insertions on my machine, I'm seeing that the Clojure
code (Clojure 1.2, java -server) takes roughly 8-20x longer (depending
on how large the hashmap is).
To test, for example, I do something like
(def ^com.justforfun.NonBlockingHashMap h (com.justforfun.NonBlockingHashMap.))
(def ^java.util.Map j (. java.util.Collections synchronizedMap
(java.util.HashMap.)))
(time (doseq [i (range 100000)] (.put h i 2))) ;900ms
(time (doseq [i (range 100000)] (.put j i 2))) ;70ms
Does this seem reasonable, or is there a better way to do this test?
Frankly, I was expecting Clojure's numbers to compare a bit more
favorably.
If you repeat the run, shoving new values into the existing hash
table, make sure to change the value you're sticking into the hash
table (Clojure optimizes when you store the same value in the hash
table that's already there).
[Code]
(ns com.justforfun.NonBlockingHashMap
(:gen-class
:implements [java.lang.Iterable]
:init init
:constructors {[] []}
:state state
:methods [[get [Object] Object]
[put [Object Object] void]
[clear [] void]
[remove [Object] void]
[isEmpty [] boolean]
[size [] int]]))
(defn -init []
[[] (atom {})])
(defn -clear [this]
(reset! (.state this) {}))
(defn -get [this k]
(get @(.state this) k nil))
(defn -put [this k v]
(swap! (.state this) assoc k v))
(defn -remove [this k]
(swap! (.state this) dissoc k))
(defn -isEmpty [this]
(zero? (count @(.state this))))
(defn -size [this]
(count @(.state this)))
(defn -iterator [this]
(.iterator @(.state this)))
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